There are testing strips that will test few things in one shot but they're highly innacurate, unacceptable for reef purposes IMO. I would suggest investing in high quality tests instead (read Salifert, Elos, Hanna photometers). The parameters that need to be tested in regular basis to achieve a healthy reef are salinity, pH, nitrates, phosphates, alkalinity and calcium (the latest two are crucial for hard corals to build their exoskeleton). Magnesium comes next, especially in larger tanks when it depletes quicker. Hope that helps